The travel agency fares you mention are most likely "consolidator" fares - special fares the agency has negotiated directly with the airline in return for a commitment to book a certain number of passengers on a particular route. These consolidator fares are negotiated for a specific time period and are renegotiated periodically. Therefore it is not surprising that the fare you got last year is not the same as the one offered this year.

Kayak and similar sites usually only search "published" fares, not private negotiated fares. That is why you will not find consolidator fares, which are often lower than published fares, on kayak.

Agencies which offer consolidator fares often advertise in the travel section of Sunday newspapers of large cities or in the classified sections of those papers. Since you are flying out of New York, I recommend you check those sections of the New York Times - they have many ads for consolidators.